Abstract
This paper summarizes the themes and recommendations that emerge from the papers presented by the Working Group on Tropospheric Ozone. In terms of current knowledge, the following are considered of particular importance: a) lack of clear evidence for a human analogue of the terminal bronchiolar and proximal acinar changes observed in the lungs of ozone-exposed animals; b) lack of evidence for a connection between the acute respiratory effects of O3 and possible chronic respiratory effects; c) need to better define the characteristics of O3-susceptible individuals; d) the lack of adequate exposure assessment tools for reconstruction of lifetime O3 exposure; and e) incomplete information on the role of other ambient environmental pollutants in the facilitation of O3 effects or as a cause of effects attributed to O3 in human populations. Based on the above, several recommendations for epidemiologic research on health effects of O3 are offered. a) Studies to investigate the existence of chronic health effects of O3 are essential, particularly those that include autopsied human lung tissue and biologic and physiologic response markers. b) Studies are needed to link acute responses with chronic effects and should include joint epidemiologic and controlled-exposure assessments. c) Studies are needed to identify susceptible subgroups. Such studies should include newly emerging biologic markers of O3 exposure. d) Accurate and precise tools for chronic O3 exposure assessment need to be developed for use in retrospective and prospective studies. e) Collaborative studies between epidemiologists and laboratory investigators are needed to develop and evaluate markers of O3 exposure and to test O3 exposure models.